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/*
 *  Licensed to the author under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package net.java.quickcheck.generator.support;

import static java.lang.String.format;

import java.util.ArrayList;
import java.util.List;

import net.java.quickcheck.Generator;
import net.java.quickcheck.GeneratorException;

/**
 * Base class for tree generators.
 * 
 * 
 * The callback order is:
 * 

 * {@link AbstractTreeGenerator#createNode()}: create current node 
 * {@link AbstractTreeGenerator#getChildCount(int, int)}: calculate number
 * of child nodes
 * (create child nodes)
 * {@link AbstractTreeGenerator#addChildren(Object, List)}: add child
 * nodes to node
 * 
 * 
 * 
 * @param 
 *            type of tree node
 * 
 */
public abstract class AbstractTreeGenerator implements Generator {

	public final static int MAX_TREE_DEPTH = 50;

	/**
	 * Create a node of type T.
	 */
	protected abstract T createNode();

	/**
	 * Add the created children to the parent node.
	 */
	protected abstract void addChildren(T node, List children);

	/**
	 * Get the number of children for the current level.
	 * 
	 * @param level
	 *            current level starting with 0 for the root level
	 * @param numberOfSiblings
	 *            number of siblings (number of siblings is 1 for the root
	 *            node.)
	 */
	protected abstract int getChildCount(int level, int numberOfSiblings);

	/**
	 * @return root node of the generated tree
	 */
	@Override
	public T next() {
		return createNodeAndAddChildren(-1, 1);
	}

	private List down(int level, int numberOfSiblings) {
		checkDepth(level);
		List result = new ArrayList();
		int childCount = getChildCount(level, numberOfSiblings);
		for (int i = 0; i < childCount; i++) {
			T node = createNodeAndAddChildren(level, childCount);
			result.add(node);
		}
		return result;
	}

	private void checkDepth(int level) {
		if (level > MAX_TREE_DEPTH) {
			throw new GeneratorException(format(
					"Max tree depth (%s) exceeded.", MAX_TREE_DEPTH), this);
		}
	}

	private T createNodeAndAddChildren(int level, int numberOfSiblings) {
		T node = createNode();
		addChildren(node, down(level + 1, numberOfSiblings));
		return node;
	}

}